Apparatus for receiving electromagnetic waves.



F. A. HART.

APIAILATIJS FOR RECEIVING ELECTROMAGNETIC WAVES.

- APPLICATION FILED MAY 6, 1910.

IIVI ENTOI? Patented Feb. 21, 1911.

T s'rA'rEs i FRANCIS A. HART, OF NEW YORK, N. Y.

APPARATUS FOR RECEIVING ELECTROMAGNETIC WAVES.

Specification of Letters Patent.

Patented Feb. 21, 1911.

Application filed May 6, 1910. Serial No. 559,768.

New York, have invented a new and useful Improvement in Apparatus for Receiving Electromagnetic Waves.

My invention relates'to these forms of syntonic receptors of Hertzian waves in which variable inductances and variable capacities are used to determine the frequency of natural response of the tuned or syntonic circuit, and it may equally well be applied to those forms of receptors in which provision is made for receiving by means of the group frequency of the radiated waves. I further aim to secure freedom from what is known in the practice of the art of wireless telegraphy as interference, that is, my invention is, so arranged as to respond very strongly to waves of a certain frequency and to the minimum possible extent to waves of other frequencies thus rendering possible the reception of messages from a distant station concomitant with the sending of messages at a slightly different wave length from the above mentioned at a near station. The means I use to attain these ends are twofold: (1) through the use of a particular arrangement of balanced and selective circuits, and (2) through the use of noninductive resistances for eliminating undesired wave lengths. These means will be successively discussed.

First: The use of a particular arrangement of balanced, and selective circuits.

In Figure 1 heretov subjoined let 1 represent the lower end of the system of conductors; used in the reception of electromagnetic waves and known briefly as the antenna or aerial. The figures represent the following l anten'na, 2, 3, 12, 13 and16 variable con densers. and 8'are primaries of an OSClllation transformer. 5 and 7 are secondaries of said transformer acting as the non-inductive resistances. 11 and 15 areresistances.

9' 'a tuning coil and 14 a suitable detector, 28 telephone, 17, 18, 19, 20, 21, 22, 23 and 24 variable contacts. Fig. 2, 27 a tuning coil. Fig. 3, 25 and 26 are condensers. The conductor from the lower end of 1. d1v1des into two parts, 3, 4, 17 and 24, second path 2 22 9 23 24.

2 and 3 are variable capacities of any type which shall prove convenient such as the mterleaved plate or concentric cylinder types and 4 and 9 are coils of conducting wire. The effective inductance of these coils may be varied by the means of the sliding contacts 17 and 24 or otherwise. Since-tl1e frequency of maximum response of a circuit is determined by the product of the inductance and capacity in that circuit, any of the previously mentioned circuitsmay be adjusted to respond to any given wave frequency within limits. In shunt across a part-of the coil 9 is the coil 8. The portion of 9 across which 8 is connected is determined by means of the sliding contacts 22 and 23, and the inductance of 8 itself is varied by means of the sliding contact 21 or otherwise. One of the terminals of coil 8 (as 23) is connected directly to the earth. Coils 4 and 8 form the primary coils of an oscillation transformer of which coil 6 is the sole secondary, that is, coil 6is coupled inductively to both coils 4 and 8 simultaneously. The inductance of coil 6may be varied by means of thesliding contact 19 or otherwise. Connected to the terminals-of coil 6 are the terminals of the variable capacity 13 and also the terminals of the detector 14 in series of which is the telephone28. The closeness of the inductive coupling'between coil 6 and coils 4 and 8 can be varied at will within limits. The circuit 6 19-13 14 28 is the actual receiving circuit and the arrangement of detector and telephone in it may be made in any of the well known ways in present use. Thus the receiving telephone may be connected directly across the terminals of the detector 14, or it may be connected in series with the same, or across the terminals of an auxiliary capacity which shall itself be in series with l4'across the terminals of 13, or otherwise.

The distribution of current and potential in a network of conductors like the above is quite complicated but the effects produced are as follows: The circuit 3 4 9 2 may be tuned to respond to the desired wave frequency which will be denoted by A, and'at sired frequency B will notaet on the circuit 6 13 14 because their amplitude (or current value) in the branches 4 and.8 will be equal but since these branches are opposed, their joint action will be null for waves of the frequency B. The coil 8 greatly increases the selectivity and is the claimed improvement. For if contacts .22 and 23 are kept y that no oscillatory current can pass in a one of said paths consisting of an inducequally distant the amplitude of the current, due to any frequency which passes through9, in the branch 8 can be regulated by moving 22- and 23 up or down coil 9. This affords a very valuable means of control of the current in 8 and hence of its neutralizing action of the efiects' produced by the frequency B (passing through 4) on 6.

Secondly: The use of own-inductive resistances for eliminating undesired wave lengths orfrequencies-It is well known circuit for which R, the resistance is greater than two times the square root of the quotient of L, the inductance of the circuit, divided by G, the capacity of the circuit. If such a state of affairs exist in a circuit that circuit is said to be aperiodic. Circuits 5 11 12, 13 and 7 20 16 15 are circuits which, through the introductions of resistances 11 and 15, or otherwise are nearly but not quite aperiodic. Such circuits are highly damped and therefore will absorb a considerable amount of energy at the frequency to which they are tunedby converting the absorbed energy into heat in the resistance of the circuit. Coils 5 and 7 are coupled inductively or otherwise to coils '4 and 8 respectively and are therefore capable of absorbing energy'at undesired frequencies and increasing the selective action of the whole arrangement.

It is by no means necessary to couple the circuits in the balancing circuit inductively as shown in Fig.1. Fig. 3 shows how the couplings may be made electrostatically through the condensers 25 and 26 whose special method of design'is clearly evident from the figure. It is also sometimes desirable to render the balancing circuits symmetrical, as shown in Fig. 2, where by the addition "of coil 2'? symmetry between the two sides of the balancing circuit is attained. In general, this complication will not be found necessary. a

I am aware that the balance method of securing freedom from interference in the reception of electromagnetic waves have been used previously, and I do not therefore claim this method broadly but I 'claim':

1. In a device for the reception of'electromagnetic waves, an antenna, two alternative paths to the earth from the antenna,

tance and a,capacity and the other of a capacity and two inductances so arranged that one of the two shall be placed in parallel with a portion variable at will of the other.

2. In a device for the reception of electromagnetic waves, an antenna, two alterna-- tivepaths to the earth from the antenna, one of said paths consisting of an inductance and a capacityand the other of a capacity and two inductances so arranged that one of the two shall be placed in parallel with a portion variable at will of the other and an oscillation transformer of which the two opposing primaries shall be respectively the inductance in that path to earth 'in which there are no parallel inductances, and the inductance which is placed in parallel with a portion of the main inductancein the other alternative path to earth.

3. In a device for the reception of electro-' magnetic waves, an antenna, two alternative paths to the" earth from the antenna, one of said paths consisting of an inductance and a capacity and the other of a. capacity and two inductances so arranged that one of the two shall be placed in parallel with a portion variable at will of the 5 other and an oscillation transformer of which'the two opposing primaries shall be respectively the inductance in. that .path to earth in which there are no parallel inductances and theinductance which is placed in parallel with a portion of the main inductance in the other alternative path to earth,

a secondary of the oscillation transformer 'comprising an inductance which together with a variable condenser, detector and telephone shall constitute the actualv receiving circuit by means of which the signals received shall become directly perceptible.

4. In a device for the reception of electromagnetic waves, an antenna, two alternative paths to the earth from the antenna, one of said paths consisting of an inductance and a capacity and the other of a capacity and two inductances so arranged that one of the two shall be placed in parallel with a portion variable at will of the other and an oscillation transformer of which the two opposing primaries'shall be respectively the inductance in, that path to earth in which there are-no parallel inductances and the inductance which is placed in parallel with a portion of the 'main inductance in the other alternative path to earth, a secondary'of the oscillation transformer coinprising an inductance, which together with a variable condenser, detector and telephone shall constitute the actuaIreceiving circuit by. means of which the signals received shall become directly perceptible, and any of said circuits having in them such a practically non-inductive and capacity free resistance as shall make the said circuits nearly aperiodic at any desired wave frequency.

5. In a'device for the reception of electromagnetic waves, an antenna, two alternative paths to the earth from the antenna,

one of said paths consisting of an inductance and a capacity and the other of a capacity and two inductances so arranged that ,one of the two'shall be placed in parallel with a portion variable at will of the other two opposing prising an inductance whieh together with a variable condenser, detector and telephone shall constitute the actual receiving circuit by means of which the signals received shall become directly perceptible, and any of said circuits having in them such a practically non-inductive and capacity free resistance 15 as shall make the said circuits nearly aperiodic at any desired wave frequency, and coupled electricallyto accomplish the same function.

FRANCIS A. HART.

' Witnesses:

.E. DEMAREsT, HARRY A. LEVINE. 

